Adding counterweight to dobsonian

[RobH2020]

Hi all, 

I've recently got a few heavier accessories for my 150p skywatcher dob: a 2" 70 degrees eyepiece and upgraded the finderscope from a 6x30 to a 9x50.

The upshot is that my scope is now very front heavy, and so always wants to tip over in the mount. I can tighten the tighteners further but makes it less smooth to move around. 

Has anyone ever added weights onto the rear end of the optical tube? Seems to me the perfect solution. 

I'm sure i could upgrade to a better mount to solve this, but I'm not looking to spend that money at the moment. 

Any thoughts on what weights to use and how to attach them?

Thanks!

Rob

[johninderby]

You can make your own weight system or buy commercial dob weights like this.

https://www.amazon.co.uk/Orion-07006-Dobsonian-Counterweight-Magnetic/dp/B07DGRHTLN

Exercise ankle weights with straps can be used or magnetic weights. Lots of ways to do it.

 

Edited March 26, 2020 by johninderby

[John]

I use a magnetic kitchen knife strip and a couple of old iron counter weights. Old kitchen scale weights would do though:

 

[F15Rules]

John,

As a complete non -Dob user, your solution looks really neat and unobtrusive. I also love the fact the weight(s) can be moved quickly and easily up and down to achieve perfect balance.

And your Dob actually looks really...er...Cool!! (Did I really say that???) 😇

Dave

[johninderby]

Or you can bolt a dovetail bar to the tube and use a small dovetail saddle with weights attached.

[RobH2020]

Ahhh magnets, of course! Can't believe I didn't think of that 😂 Thanks everyone!

[johninderby]

Yes the Skywatcher dobs use steel tubes so magnets work well. Orion Optics UK dobs like Johns have aluminium tubes so can’t attach magnets directly hence the kitchen knife strip.

Edited March 26, 2020 by johninderby

[westmarch]

Alternatively, attach a heavy biker’s chain to the rear end of the dob. The lower the scope elevation, the greater the amount of chain suspended to balance the increased moment from the eyepiece end.

John

[davhei]

Here’s yet another solution I slapped together. Got a number of metal plates with M5 holes from the hardware store. Had two neodymium rubber clad magnets with M5 threads that I fastened to a stack of plates using two bolts. Finally put some duct tape around the arrangement to soften out the edges.

Perhaps not that elegant but seems to balance the scope nicely. Counterweight weighs around 2,2 kg which seems enough for balancing my moonlite focuser with spacers and my heaviest eyepiece which is in fact not that heavy at just below 0.5 kg.

 

Edited July 2, 2020 by davhei

[davhei]

Had a chance to try out this counterweight setup last night. Was doing mainly planetary observing at low altitudes that previously tended to cause the scope to slowly tilt downwards.

This time the balance was excellent! Could loosen the handles on the dob almost fully and still it maintained position. What a joy! Tried some deep sky when it got dark enough and picked out M57, the double cluster and Albireo reaching altitudes of +60 degrees and still well balanced. What a difference counterweighting does. Very happy about it!

Edited August 1, 2020 by davhei

[Starwatcher2001]

My dob used a plywood tube, so I glued a couple of strips of velcro down the back and used a tupperware box of lead with velcro on the bottom. I like hi-tech solutions.

[Spile]

Sorry to necro-post but I am interested in finding out more about counter balancing a Dobsonian.

The Telrad and Zoom eyepiece on my 8" Skywatcher means that in the horizontal position there is a change in the centre of gravity. I have therefore (temporarily) added a weight to counter this.

However, I was observing without the counter weight a few nights ago and I cannot say I noticed a difference. I am wondering if counter balancing a 8" OTA may be unnecessary as...

• Most observing taking place with the OTA closer to the vertical rather than horizontal position.
• The friction of the handles picking up any slack anyway.

Thoughts welcome as I am not convinced that lugging a dead weight down my garden is worth it.

 

[John]

The "nose droop" tendency gets gradually less as the scope is pointed upwards. When I'm observing an area around the zenith I don't need any counterweight even with my heaviest eyepiece. When observing something close to the horizon (ie: Sirius) I need both counterweights.

Thats why the length of chain approach works quite well - the lower the scope is pointing, the more chain is off the ground and vice versa. It's not the neatest solution though.

 

Edited February 15, 2021 by John

[Stu]

I made a solution for my 8” f8 using a couple of spare tube rings I had, plus a dovetail. I can slide the weight up and down, or remove it completely when observing nearer the zenith. Works quite well, not as neat as John’s magnetic rack but not too bad.

 

[Ricochet]

4 hours ago, Spile said:

Thoughts welcome as I am not convinced that lugging a dead weight down my garden is worth it.

I agree. I tried that once and discovered that I used the telescope less often. I've added a bungee based system to mine so that the force exerted varies automatically with the telescope angle. It's not obvious from the photo below, but at high altitudes the bungee actually pulls the front of the telescope "down" to counteract the weight of the finders, focuser and eyepiece(s) hanging over the back of the tube. 

[AlexK]

It all depends on your telescope construction. But as soon as you have a classic Dobsonian without various braking handles recently emerged on some designs from China engineers the CoG (Center of Gravity) maintenance is unavoidable as soon as you upgrade your stock cheap and small and thus lightweight eyepieces with something with more expensive glass inside.

I do. So for over 10 years I've been using a simple DIY solution made from an old small GEM counterweight puck and two magnets from dead 3.5" computer hard drive:

Just a piece of masking tape over magnets to prevent OTA scratching. It holds anywhere on the OTA. Ideally, it should go on the opposite side from the focuser. To keep the CoG below the altitude axis, but that's an awkward location to reach, so I'm using it on the top side of the OTA most of the time, which means I have to remove it closer to Zenith.

Lately, I'm using that puck in the special cradle with the pocket for the USB Powerbank, which is powering the mirror cooler, QuInsight pointer, and other low power electronics on the scope. That helps keeping the counterweight higher at hand (no image yet, but here is the 3DP draft of the cradle:

The root principle of the Dobsonian mount is that the CoG is always below the Altitude axis line and the gravity vector down from it is always exactly in the middle between Altitude PTFE tabs. That the key not only for its rock-solid stability but also to the perfect fluidity of rocking forward and backward motion.

Edited February 15, 2021 by AlexK

[Spile]

19 hours ago, AlexK said:

the CoG (Center of Gravity) maintenance is unavoidable as soon as you upgrade your stock cheap and small and thus lightweight eyepieces with something with more expensive glass inside.

I don't think the Baader Hyperion IV counts as stock, cheap or small. As I said, with the Telrad yes it does change the centre of gravity but I have yet to be convinced that with a 8" OTA it is worth my doing anything about. I will keep reading others experiences.

[AlexK]

That Baader Zoom is actually considered lightweight, as all of its lenses inside are under 1.25" mark (or close) that's in fact a 1.25" EP (just with the stock 2" adapter attachment). Telrad is very lightweight as well (single lens), especially if you use it with Lithium cells (by the way, these are bar none in weight and longevity departments to the task, except for the external USB power cable of course). So you are good.

And you are definitely don't have to do anything with your mount until something starts annoying you.
I.i.r.c. SW S line dobs are using the side brake mechanism to adjust the friction in altitude as their mount trunnions are rolling on plastic wheels there. That one of the "improvements" from China engineers to the classic Dobsonian design. I would be personally annoyed by the need to tweak it with that handle constantly

Edited February 16, 2021 by AlexK